I am messing around with my alternator on my 71 charger. The alternator has 3 connections coming off of it. My understanding is these are called a BAT terminal, No1 Terminal and No2 Terminal. So why are there 3 terminals rather then just a single one delivering the current? I am pretty sure i am overlooking something basic.

Dual field.

edit: This is my understanding of how they work and why you need the extra wiring...

Mopar alternators, unlike the preceding generators don't use permanent magnets in their construction. The electric "field" that is created when a 12 volt source is supplied to the connections you see marked as 1 & 2, essencially creates electric magnets in the housing around the spinning stator, which are used with the stator to generate electric A/C current. That current is then passed through a device with diodes called a rectifier to change it to DC current.

They used to use single field alternators, but as the need for more electrical power grew, the addition of the second field to create dual field system was an easy way to trick the alternator into thinking it was two alternators by effectively doubling the amount of electric magnets inside the alternator.

By controlling(switching on and off) the relatively lower field voltage to the electric magnets, the higher current output of the alternator can be controlled and regulated to adjust the alternators output.

This design eliminates the need for a switch on the high current output side of the alternator to control voltage, which would be large and wear out quickly, especially as the output of electrical systems increased.

FYI you can put the blue and the green field wires on either of the alt small field terminals though they were all done the same way on the assembly line for standardization and if your wire/terminal ends are hardened/set in a certain bend whichever choice/route lets them lay/look the best is fine.